Diabetic retinopathy is the leading cause of blindness in the working age American, age 20-64 years. Although impairment of visual function in the advanced form of diabetic retinopathy has been extensively studied, visual function in background diabetic retinopathy (BDR) has not been well examined. Patients with background diabetic retinopathy have good visual acuity but the mere appearance of dot hemorrhages, microaneurysms, and hard exudates may herald underlying retinal dysfunction. We hypothesize that the electroretinogram (ERG), as a measure of visual function, may detect changes in early BDR. Once these changes are recognized, we may further understand the electrophysiology of the vascular changes in early diabetic retinopathy. The electroretinogram measures electrical activity within the retina after stimulation by light. The function of the photoreceptor (a-wave) and inner retina nourished by the retinal vessels (b-wave and oscillatory potential) may be examined by using the ERG. In preliminary studies at the Joslin Clinic, Dr. Wu has recorded ERGs from eyes with BDR (13 pts), no diabetic retinopathy (NDR 12 pts), and normal, nondiabetic controls (C, 12 pts). We found that the ERGs of the C and NDR eyes showed no statistically significant differences. Implicit times in the BDR eyes were greater than NDR eyes for the scotopic blue b-wave (BDR: avg=99.1 msec, sd=26.7; NDR: avg-77.6 msec, sd=18.8) (p<0.01) and 30 Hz flicker (BDR: avg=44.0 msec, sd=22.3; NDR avg=31.2 msec, sd=4.5) (p<0.02). These results suggest that there are detectable changes in the ERG which may correlate with the degree of diabetic retinopathy even in the early stages. To date, there is no published data on ERG changes, in dilated, dark adapted eyes with BDR or in diabetic patients with no retinopathy. Our data suggests that the retina may seem compromised despite minimal fundus findings and good visual acuity. The proposed project will extend these initial observations by correlating the ERG with visual acuity and is fundus findings in patients with early BDR and no diabetic retinopathy and normals. It is the longterm goal to use the ERG to differentiate among the early diabetic retinopathy patients who have good visual acuity, which may have more widespread vascular damage than we hope to follow longitudinally those patients to find electrophysiologic markers of progression of diabetic retinopathy.